Preliminary evidence from neurological patients with lesions and from normal individuals studied with PET, suggests that the normal process of retrieving words which denote concrete entities depends on multiple regions of the left cerebral hemisphere located outside the classic language areas. Moreover, at the level of large-scale systems, there appears to be an intriguing and principled relationship between the anatomical region and the kind of item being named. Drawing on these findings, we have developed a set of hypotheses regarding the neural basis of the process of lexical retrieval. In this Program, we propose to investigate these hypotheses in both English and American Sign Language (ASL), using the same approach - functional imaging - and the same paradigm - [15-O] H2O - PET activation studies. The Program brings together investigators from two institutions, diverse fields of expertise, and diverse human populations of normal hearing, deaf, and neurological patients. Results from the investigations proposed here promise to broaden the currently limited knowledge available on the neurobiology of language. Such new knowledge is critical to further the understanding of communication disorders in both the normally hearing and the deaf, and is indispensable for the development of effective rehabilitation strategies for aphasics in both auditory-based and sign languages. The knowledge gathered here can also be used to constrain ongoing theoretical and empirical work on the linguistic and cognitive aspects of the lexicon.